1. Field of the Invention
The present invention relates to measuring the acid and/or water content of nonaqueous media and measuring the acid content in the presence of water of such nonaqueous media. In particular, the present invention relates to monitoring the quality or condition of engine oil.
2. Description of the Related Art
Acid species in nonaqueous media, such as hydrocarbon-based oil, cause gelling and change the viscosity of the oil so that there is an overall loss of lubricity. Oil in an engine, for example, containing an acid species will not properly coat the engine's moving parts causing the parts to seize up and prematurely fail. Moreover, acid species in hydrocarbon-based oil causes corrosion of the engine's metallic parts.
Water accumulation in engine oil is problematic also. Depending on the geographic region and seasonal weather conditions, water may accumulate in the engine oil faster than it is evaporated. Prolonged exposure of the engine's moving parts to accumulated water will cause corrosion. Moreover, accumulated water in engine oil will remove oil additives and preservatives, which function to neutralize acid species.
The quality of oil is particularly important in the automotive industry. Automobile manufacturers recommend that a vehicle's oil be replaced on a regular basis based on the number of miles the vehicle has been driven. Typically, the actual condition of the oil at the time it is replaced is not known. If the oil should degrade prematurely, the vehicle is operated with the degraded oil at least until the next regularly scheduled oil change. On the other hand, if the vehicle is operated under much less rigorous conditions, including weather conditions, or conditions that are favorable to an extended lifetime for the oil, the oil may be replaced and discarded prematurely, which increases the cost of operation and causes unnecessary environmental problems. With respect to water accumulation, a vehicle driven in a cold winter climate for only a few miles a day, will accumulate water in the engine oil to a much greater extent than a vehicle driven in a warmer climate. Nevertheless, the recommended schedule for changing the oil in the vehicle is the same.
Other important areas of application include diesel engines and automatic transmission fluids. In the former case, diesel fuel contains significant amounts of organo-sulfur compounds, which degrade through use and are oxidized eventually to sulfuric acid. Not only is sulfuric acid highly corrosive, but it causes increased operating temperatures of the oil. Automatic transmission fluids are also hydrocarbon-based materials and they thermally oxidize to carboxylic acids leading to similar eventual operating problems.
It would be desirable if the engine oil in a vehicle could be monitored and replaced only when the oil has degraded to a level which is rated unacceptable to the proper operation of a vehicle.
One monitoring device for indicating when oil has degraded to an unacceptable level is known from U.S. Pat. No. 5,089,780 issued to Megerle on Feb. 18, 1992. Megerle discloses a sensor and system for monitoring the accumulation of contaminants in oil. The contaminants must have an electrical conductivity which is different from the oil. An alternating current conductivity is measured by an electrochemical cell and an indication of the amount of the contaminants present is provided. The conductivity cell includes concentric cylindrical electrodes mounted on a plug or other structure so that they can be immersed in the engine oil. The plug can be mounted in the oil sump, or oil stream, of the engine. One electrode is connected to an AC conductivity measuring device which is connected to a warning light or display device that provides an indication of the oil conductivity. The ability and usefulness of the Megerle device for monitoring the accumulation of water is not known. Moreover, contaminants dissolved in accumulated water in the oil are less likely to be detected with an electrochemical cell.
Conductive polymers have been used as the active material in sensors to detect acidity, or more specifically, pH in aqueous and highly polar systems. Conductive polymer acidity sensors are advantageous because they are compact, simple, inexpensive, and easy to make. A number of high sensitivity prototype sensing devices have been reported using the conductive polymer, polyaniline, as the active sensing material. For example see J-C. Chiang and A. G. MacDiarmid, Synth. Met., Vol. 13, 193 (1986). These range from chemical gas sensors to pH sensors in aqueous solutions.
Yodice et al., U.S. Pat. No. 5,023,133 issued Jun. 11, 1991, discloses an acid sensing device for nonaqueous media, such as motor vehicle lubricating oil. The devices comprise an organic polymer, such as polyaniline or polypyrrole, which is capable of accepting protons. However, Yodice et al. are silent with respect to the ability to monitor water content and acid content in the presence of water.
Y. Maeda, European Patent Application No. 0 442 314 A2, published Aug. 21, 1991, disclose an apparatus for detecting deterioration of lubricating oil. The apparatus comprises a membrane of polyaniline which is treated with an electrical oxidation and an electrical reduction that is immersed in lubricating oil. The electrical resistance of the membrane changes with changes in the amount of acid in the deteriorating lubricating oil. The deterioration is monitored by measuring the electrical resistance between a pair of electrodes.
Maeda et al., like Yodice et al., are silent with respect to a device which comprises a conductive polymer for accurately monitoring water content and acid content in the presence of water in such nonaqueous media.
Therefore, there is a need for a compact, low cost sensor having a conductive polymer as the active element that is adaptable for a method of monitoring acid content, water content, and/or acid content in the presence of water in nonaqueous and nonpolar media, such as hydrocarbon-based oil.